In a large saucepan, add in the heavy cream and milk. Place over medium heat and let it heat up to almost boiling. There will be puffs of steam and small bubbles on the edges of the saucepan.
Meanwhile, add yolks to a small bowl. Set aside.
In separate bowl, add in sugar, cornstarch, chocolate malt powder and salt. Whisk to combine.
Combine the dry ingredients into the egg yolks and stir to combine.
Add about 1 cup of the hot milk into the egg mixture and start whisking immediately.
Once the milk and egg mixture are combined and completely incorporated, add the mixture back into the saucepan.
Place the heat over medium/high. Mine was closer to medium. Whisk often until it begins to thicken.
Once it starts bubbling and becoming thick, whisk constantly to avoid burning. It took mine 30 minutes to thicken completely. It will be quicker if you have the heat higher. The filling will still be pourable.
Remove from the heat and add in the vanilla and cold butter. Whisk until the butter is incorporated.
Pour the mixture into a bowl and cover with plastic wrap. Press the plastic wrap down onto the surface of the pudding. Place in the fridge overnight to cool and set up.
Just before assembling the pavlova, put the ganache together.